For the purpose of supplying coolant or lubricant, cutting tools comprise internal cooling channels through which the coolant is channelled to the drill tip. Apart from the function of cooling and lubricating the drill tip, the coolant also has the function of improving chip removal.
In order to remove the chips from the cutting groove, the coolant has to be fed in at times at high pressure, especially in the case of deep-hole drilling, wherein the internal cooling channel i.e. the drill has to be able to withstand corresponding pressures without being destroyed. In particular as part of minimum quantity lubrication, a process which is becoming widespread, there is a desire to design the cooling channels so as to provide the largest volume possible. In addition, there is a need to be able to make ever smaller and longer drill holes. However, with increased lengths and reduced diameters of a drilling tool, it becomes increasingly difficult to dimension the internal cooling channels in such a way that corresponding coolant throughput or coolant pressure is provided, without the sturdiness of the drill being negatively affected. For, the size of the cooling channels is limited by the distance to the drill back or the cutting space. If the lands are too thin, cracks and tool breakages occur. In the case of multiple-cutting tools, the cooling channels must also be spaced apart from each other by a certain minimum distance, otherwise impediments result in the face geometry of the drill, i.e., for example in the transverse cutter or in a point shape.
Known drills usually have internal cooling channels with circular sections. Apart from this, in principle, methods are already known with which sintered blanks with elliptical cooling channel cross sections can be produced, for example from DE 42 42 336 A1. U.S. patent specification U.S. Pat. No. 2,422,994 already mentions a cooling channel profile design other than a circular design. Furthermore, cooling channels with a trigon profile in the form of a isosceles triangle with rounded corners have been proposed, for example in patent specification DE 199 42 966 A1.
Apart from this, in DE 3629035 A1, a double cutting drill with a cooling channel profile in the form of an isosceles triangle with rounded corners has been proposed, with which a position of the internal cooling channels close to the center is to be possible, which position makes it possible to provide central delivery from the cooling channel at the conical end of the drill.